The present invention relates to an artificial foot for a leg prosthesis comprising a foamed plastic moulded foot portion with a plate-shaped, metallic reinforcing member embedded within its plantar area which, in the ball area, is constructed with a curved section extending in the manner of a ball of the foot for supporting the rolling function of the foot and with - serving in each case as an elastic, yielding cushioning - a forefoot core and a function core consisting of a tongue disposed within the heel area, the function core and the reinforcing member being rigidly interconnected. Polyurethane foamed plastic which possesses the advantage of a light weight has been employed for artificial feet for a long time.
In order to enable the artificial foot to approximately perform the function given in a natural foot, by way of example, in U.S. Pat No. 3,335,428, a leg prosthesis foot portion has been proposed that is constructed of elastic plastics of varying hardnesses.
In addition, from the DE-PS No. 354 246, an artificial foot is known in which, within the plantar area of said artificial foot, a metal bar is embedded. This artificial foot is intended to enable a foot or a leg amputee to take long strides, since taking of long steps involves the oblique rearward displacement of the lower leg, that is to say the yielding of the heel of the foot which rests on the ground with its entire base. It is intended, moreover, to bring about the easy straightening up again of the lower leg without the same exceeding the vertical position, while the forward displacement of the body weight and the raising of the heel is intended to be rendered possible by the normal flaxibility of the metatarsal and dactylar section of the artificial foot. This flexibility is intended to be obtained by embedding a spring plate extending through the plantar and the heel sections. In order to now produce the oblique rearward projection of the lower leg, this known embodiment of an artificial foot provides a connection between the rigid lower leg and the spring plate in which the sailient portion, from its upright position, moves rearwardly in the fashion of a rocker and, when the body weight is moved in the forward direction, again assumes the first position. This rocking motion is effected in that the rigid lower leg which tapers in a wedge-like manner, is seated in a saddle, the one slope of which is formed by the instep of the artificial foot and its counterslope by a branch of the spring plate. For additional cushioning, a compressible wedge-type cushion, e.g. of soft rubber, is disposed between the branch and the spring plate proper. In order to prevent any undesirable noise being produced when the front wedge surface on the salient portion impinges upon the foot, the forefoot or the metatarsus consists of a pliant or readily compressible, at any rate noise-deadening material, preferably felt. The abutment surface of the lower leg is also covered with this material. In this artificial foot, the branch of the spring plate is rigidly connected to the rear wedge surface of the lower leg. In this case, however, the branch is not bent sharply because a rocking or swaying motion is aimed at. For this reason it is attached to the plate so as to glide with its bend.
In this artificial foot, a steel spring with resilient properties is thus inserted which extends as far as to the forefoot. However, from a constructional point of view, the most important differences in elasticity between the metatarsus and the forefoot have not been taken into account in this case. However, the steel spring employed does not render a natural rolling function possible, moreover, the connection problems between the various materials are not solved in the elastic sphere. Furthermore, from the DE-PS No. 361 972, an aritficial foot is known which is provided with a longitudinal spring cushioning means consisting of several leaf springs arranged in steps relative to one another, the leaf springs of which are secured with their rear extremities to the underside of a rigid block forming the rear foot portion which, however, is separated from the sole of the foot by an intermediate layer, while the spring front extremities which are run downwardly in a suitable double curveature, press directly upon the sole which is expediently covered with a protective plate. In this artificial foot, too, an attempt is made to control the movements of the foot by means of a metal spring; but it does not allow any mobility within the metatarsophalangeal area.
In an artificial foot for leg prostheses known from the U.S. Pat. NO. 2,556,525, a rigid, but flexible plastic member is inserted into an outer foamed plastics moulded foot portion, said member extending over the entire length of the foot, a metal insert of spring steel being embedded in this rigid but nevertheless flexible plastic member. Even if an internal, partly flexible plastic member with a metal insert of spring steel is used in this known artificial foot, it is not possible with this artificial foot to place the rolling function of the foot onto the division-by-three line provided by nature. For the rest, the metal insert is also run as far as to the point of the foot. In spite of the use of a flexible plastic member and of a metal insert fabricated from spring steel, an adequate mobility within the metatarsophalangeal joint, as exists in nature, is not possible. The important bending in the metatarsophalangeal joint has not been taken into consideration in this known embodiment and, due to the structural configurations, is not possible either.
In order to provide an artificial foot for leg prostheses with a rolling resistance of high elasticity and a facility for bending in the metatarsophalangeal joint for a relatively long period, in the DE-PS No. 23 41 887, the artificial foot described in the beginning has been proposed. In this artificial foot the forefoot elasticity is ensured by the use of a homogenous Vulkollan (elastomer) member, that is to say, a resilience is taken into consideration in the forefoot which exceeded the cushioning effects produced until then. It is true that up till now it had not been possible to functionally utilize the advantages provided by this resilience in its physical influence factor on the gait or walk image.
It therefore is the object of the present invention to develop the artificial foot stated in the beginning in such a way that a substantial degree of metatarsal elasticity is ensured up to a maximum rolling moment of 120 Nm even at a continuous stress of up to 3 million load alternations without having to forego the advantages offered by the artificial foot known from the DE-PS No. 23 41 887.